Arc confinement in lightning arresters



May 26, 1959 J. w. KALB ARC CONFINEMENT IN LIGHTNING ARRESTERS Filed March 29. 1955 g2, 4| 2a 40 G- s v IIIIS Fig. 3

INVENTOR. JOHN W. KALB.

iam m ATTORNEYW .U itd Slams a v 2,888,608 ARC CONFINEMENT 1N LIGHTNING ARRESTERS John W. Kalb, Wadsworth, Ohio, assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation of New Jersey Application March 29, 1955, Serial No. 497,496 4 Claims. (Cl. 315-36) This invention relates to protective devices such lightning arresters, and more particularly to an improved spark gap device which has a high power follow current interrupting ability.

it is a general object of the invention to reduce the size of lightning arresters or alternately to increase the current interrupting ability of such lightning arresters of a given size.

Another object of the invention is to increase the current interrupting ability of the spark gap device of a lightning arrester.

Still another object of the invention is to make lightning arresters more compact and eflicient by preventing arcing across the several electrodes of the spark gap device of the arresters.

Still another object of the invention is to provide an arc barrier for' spark gap devices which comprise a column of spaced electrodes of the kind in which arcs are formed between the successive pairs of electrodes and which function electrically to form a plurality of series connected arcs.

Lightning arresters having a spark gap device connected in series with a voltage sensitive resistance element are known in the art and are shown, for example, in U.S. Patent 2,324,108 issued July 13, 1943 to S. C. Pyk and U.S. Patent 2,640,096 issued May 26, 1953 to John W. Kalb. The spark gap device of these arresters is formed of a number of electrodes which are spaced one from another by separating members to form a number of gaps which are in series each with the other and with the resistance element.

The electrodes of the spark gap device are, as set forth in the patents referred to above, formed of disc-like pieces of hard brass. The disc-like pieces have portion projecting in alternate directions from the body of the disc to receive the separating members on the one side thereof and serve as are surfaces on the opposite side thereof. The gap device is thereby made relatively compact in an axial direction and may be made to have a relatively high current capacity-for the size thereof. This is an aspect of great importance, inasmuch as, for the high voltages which are employed for long distance transmission lines, lightning arresters would otherwise be solarge as to be impractical.

The considerations referred to above have to do with the longitudinal extent or height of the arrester and constitute a limitation upon the design thereof. Correspondingly, similar limitations exist as to the lateral extent, e.g. the diameter and periphery of the spark gap device and the arrester housing. This latter limitation is brought about by reason of the fact that under certain conditions the arcs formed between the adjacent gap electrodes tend to wander from the place of initial formation, usually as a result of the forces set up by local magnetic fields between the adjacent electrodes. These forces are a function of current density in the arcs and, if that density is suificiently high and, if the place of initial spark over is sufficiently close to the electrode, the arc may move to 7 2,888,608 t t 4Mer 6tt??? the cdge'of the electrode and there combine with the similar are between the adjacent pairs of electrodes. Because of the influence of the magnetic fields produced by the arcs between the outer edges ofthe electrodes and the inherent voltage-current characteristic of the arc, there will be a tendency for the arc or combined arcs to recombine into a single arc across the entire length of the spark gap device with a resulting impairment of the current interrupting ability of the gap'device and of the arrester. I

It has," therefore, been a general problem of the art to reduce the size of such lightning arresters without impairment of the current interrupting ability which results from are over between the edges of the gap electrodes.

In accordance with the present invention the prevention of such are over may be accomplished by covering the entire gap device by means of glass cloth in such a way that the outer edge of the electrodes are firmly con-' tacted between the cloth. The cloth acts as a barrier to stop the arc just short of the edges of the electrodes while being sufliciently porous to permit the escape of the ionization products generated between the electrodes by the arcs. Thus, the invention may be practiced by providing a sleeve of glass cloth which is drawn over the electrodes of the gap device or a sheet of the cloth may be wrapped about the gap unit and attached to the electrodes.

The invention, together with further objects, features and advantages thereof may be more clearly apparent on consideration of the detailed specification and claims taken in conjunction with the appended drawings in which:

Fig. 1 is a sectional view of the improved arrester of the invention;

Fig. 2 is a view showing particularly the arrangement of the glass cloth over thespark gap device; and

Fig. 3 is a sectional view of a portion of the gap device illustrating the use of a cloth sleeve as an arc barrier.

Referring now to Fig. l, the arrester 10 of the invention comprises a cylindrical porcelain member 11 which has a hollow bore 12 for enclosing the operative elements of the arrester. The arrester includes a plurality of non-linear resistive valve elements 13 and 14 at the upper and lower ends of the arrester respectively, a gap assembly 15 and a spring 16 for holding the valve elements and the spark gap assembly in contact with each other and with the end of the housing. The housing.

incorporates two metallic end plates 17 and 18 which serve as supports for the arrester and has terminals for connecting the arrester to the power line or other external circuit for which the arrester is employed as a protective device and to ground. V

Each of the valve elements 13 and 14 comprises a substantially homogeneous block of silicon carbide or the like and has two flat metallic plates at the ends of the block. Thus, the several valve elements in the gap assembly are connected in series with each other and to the end plates by the engagement of the metallic plates. The metallic plate 19 at the bottom end of the lowermost valve block is engaged with an annular member 20 which bears upon a metallic closure member 21 and is, in turn, in electrical contact with the terminal 18. The closure member 21incorporates a diaphragm 22 of thin copper which is adapted to rupture when the pressure within the housing exceeds in contact with the lower plate 27 of the lowermost of the two upper valve blocks 13. The upper plate 28 of the uppermost of the valve blocks 13 bears against a sealing member 40 which is, in turn, in electrical contact with the annuiar spring member 41 and the terminal 17. The sprin 16 maintains an adequate electrical connection between the several valve blocks, the components of the spark gap assembly and the members associated with the terminals 17 and 18.

The sealing arrangement between the terminals 17 and 18 and the housing 11, as well as the frangible diaphragm 22, is described in detail in US. Patent No. 2,640,096 referred to above.

The spark gap assembly 15 comprises a column of spark gap electrodes 30 which are held by a ceramic rod 31 extending longitudinally through the electrode members. The electrode members are maintained in vertically spaced relationship by appropriate separating members 32 which are disposed about the rod 31 and held between projecting or dished portions of the electrode members. The separating members 32 are ordinarily formed of high resistance material and comprise a resistance grading arrangement for the several electrodes of the gap device.

Each of the electrodes 30 incorporates a plurality of projections which extend alternately in opposite directions from the body of the electrode member. The surface of the projections on the convex side thereof constitutes the arc surfaces of the gap unit formed by each'pair of electrodes, while the associated concave side of the projection serves as a recess for holding the separating members 32. The construction of the electrodes is described in detail in the patents referred to in the introductory portion of the specification.

When the arrester discharges because of an excessive accumulation of static electricity in the line to which the arrester is connected, arcs are formed between the opposed arc surfaces of the several pairs of electrodes 30. The arcs of the several pairs of electrodes are effectively in series so that the entire gap assembly exhibits a certain arc resistance in normal operation. However, because of the local magnetic fields set up between the pairs of electrodes by the arcs of those electrodes, and particularly when high current densities are utilized, the arcs may travel or wander from the arc surface proper and be maintained between the bodies of the electrode members. Under these circumstances the arcs may travel outward toward the edges of the electrodes so they may readily combine to form short circuiting arcs between several of the electrodes and, particularly, a single arc across the entire spark gap device. As a result of such formation of a single arc across the entire spark gap device, the current interrupting ability of the gap device and of the arrester proper is substantially impaired.

In accordance with the present invention, the formation of such short circuiting arcs is prevented by means of an arc barrier about the outer periphery of the gap electrodes. This barrier comprises a sleeve 33 of glass cloth which is drawn over the gap assembly so that the natural resilience of the cloth holds it against the edges of each of the electrodes.

As a result of this arrangement, the wandering arcs which are formed between the electrodes under the above described conditions, are effectively stopped short of the edges of the electrodes and cannot jump to non-adjacent electrode edges. The use of glass cloth is important inasmuch as the cloth stops the arc and yet is sufficiently porous to enable the ionization products to escape from between the electrodes and into the housing proper.

The spark gap device may be constructed by drawing the glass cloth sleeve over the electrodes after they have been assembled on the center rod 31 with the separating members in place, or, alternatively, a sheet of the glass cloth may be wound tightly around the electrodes and the free end of the sheet bonded to the previous turn. In either case, the upper and lower ends of the cloth may be allowed to project beyond the end electrodes or may be bonded or otherwise attached thereto as shown at 34 and 35 in Figs. 1 and 2.

The advantages achieved by the use of a sleeve of glass cloth will be more readily apparent upon consideration of Fig. 3 where it will be seen that the natural elasticity of the woven material is such that the cloth is held firmly against the outermost edges of the gap electrodes. There is, consequently, little need for attaching the upper and lower ends of the sleeve to the uppermost and lowermost electrodes and the sleeve may project beyond the end electrode 36 as is shown at 37. A glass cloth which is woven in sleeve form is commercially available so that the practice of the invention is simplified.

It is to be understood that the foregoing description is not intended to restrict the scope of the invention and that various rearrangements of the parts and modifications of the design may be resorted to, giving effect to a liberal interpretation to the claims as herein set forth.

I claim:

1. A spark gap device for lightning arresters comprising a column of separate disclike electrodes spaced each from the other and separating members between successive electrodes, each of the gap electrodes having alternating oppositely directed projections disposed peripherally about the electrodes and inwardly from the outward extremities of the electrodes, each projection serving as a recess for holding a separating member on one side and as an arcing surface on the opposite side, and an arc barrier comprising a porous cloth of fibrous heat resistant insulating material constituted by woven glass fibres disposed about the entire periphery of the electrodes and in contact with the outer extremities thereof for confining the several arcs to the electrodes to which they are formed and preventing arcing across the electrodes at the extremities thereof whereby the current interrupting ability of the gap device is maintained for relatively high current densities through the device.

2. The invention in accordance with claim 1, in which the glass fiber cloth is in the form of a sleeve and has a natural resilience such that the inside of the sleeve is held in intimate engagement with the extremities of the electrodes.

3. The invention in accordance with claim 1, in which the glass fiber cloth is in the form of a continuously woven sleeve arranged over the exterior of the electrodes and elastically engaged with the extremities thereof.

4. The invention in accordance with claim 1, in which the glass fiber cloth is attached to the end electrodes of the assembly about the periphery thereof.

References Cited in the file of this patent UNITED STATES PATENTS 493,314 Thomson Mar. 14, 1893 1,171,598 DeForest Feb. 15, 1916 2,253,719 McMahon Aug. 26, 1941 2,393,164 Hobson Jan. 15, 1946 2,640,096 Kalb May 26, 1953 2,664,518 Eldridge Dec. 29, 1953 

